In the past, various processings are known to be performed on an image signal for a purpose of image quality improvement. For example, the processings include an enhance processing, a noise reduction processing, an aliasing prevention processing, or a motion adaptation interlaced to progressive (“I/P”) conversion processing. The enhance processing is a processing for enhancing a high frequency component of the image signal to enhance a contour of an image. The noise reduction processing is a processing for suppressing a noise included in the image signal. The aliasing prevention processing is a processing for removing with a filter, a frequency component which becomes a cause of an aliasing distortion. The I/P conversion processing is a processing for changing an interlace signal to a progressive signal.
In the past, changing of the above-mentioned processings on the image signal in accordance with a type of the image signal is known. For example, Japanese Unexamined Patent Application Publication No. 2006-260520 (“the '520 publication”) discloses classifying image signals into two types, a moving image and a still image, and changing the enhance processing depending on whether the image signal is a moving image or a still image. However, among image signals classified as moving images in the past, in addition to an image signal being a moving image from the beginning, there can also be image signal generated by being subjected to a processing for adding a motion to the image signal of the still image.
In this case, as the processing for adding the motion, a movement of a read position at a part of the still image, or a magnification or a reduction, may be performed. In a case where the read position at a part of the still image is moved, a perceived amount of aliasing of the sampling on a screen may vary depending on the case of moving in an integer pixel/frame and other cases.
In some cameras for picking up a still image, the number of pixels may be over 1000 million pixels. In general, a still image camera has a higher resolution than a moving image camera. An image obtained by moving the read position at a part of the still image has a higher resolution than an image obtained from the moving image camera, and the noise may stay at the same position with respect to a subject.
From the above, as described in the '520 publication, with the signal processing only based on classification into the two types including the image signals of the moving image and the still image, in view of securing of the acutance, the perceived amount of the noise, and the perceived amount of the aliasing distortion, an optimal image quality cannot be obtained.
It is accordingly a primary object of the present disclose to perform an image signal processing so that an optimal image quality can be obtained all the time.